Descent rate in propliners and instrument flight rules

[Cas141]

Hello

I have recently taken to flying propliners , from jetliners, and I use instrument flight rules.

As you know, in fsx, the default ATC instructs when and to what height to descend to at which heading etc- until finally putting you on the glideslope.

Typically in a jet, the descent rate is about 2000 ft per min.

I am concerned that if I descend in a propliner at (the recommended) 700 ft per min, that the fsx ATC will not be able to "handle" that and I will miss the glideslope.

Even now, in the jet, sometimes the ATC tells me "to expedite my descent to xxxxft" In other words, hurry up!

 

I am a bit wary that the default ATC is sophisticated enough to sus that I am flying a propliner and therefore they will instruct the descent to begin earlier to allow for the shallower descent rate.

 

Has anyone found any problems approaching with default ATC , as described above? Or any advice or tips for a new propliner pilot😀

Thanks

[mrzippy]

When flying the propliners I would set my descent rate to about 1400 feet/min. I found that was adequate to get me down to the assigned altitude in plenty of time. Depending on my cruise altitude, I would normally request a descent on my own rather than waiting for ATC to begin a descent. I would initiate the start of my descent about 120 miles from destination. I also did the same thing when flying jet tubeliners.

 

That way you can beat ATC at their own game and easily be at the proper altitude for your approach to your destination airport.

[mallcott]

Hello

I have recently taken to flying propliners , from jetliners, and I use instrument flight rules.

As you know, in fsx, the default ATC instructs when and to what height to descend to at which heading etc- until finally putting you on the glideslope.

Typically in a jet, the descent rate is about 2000 ft per min.

I am concerned that if I descend in a propliner at (the recommended) 700 ft per min, that the fsx ATC will not be able to "handle" that and I will miss the glideslope.

Even now, in the jet, sometimes the ATC tells me "to expedite my descent to xxxxft" In other words, hurry up!

 

I am a bit wary that the default ATC is sophisticated enough to sus that I am flying a propliner and therefore they will instruct the descent to begin earlier to allow for the shallower descent rate.

 

Has anyone found any problems approaching with default ATC , as described above? Or any advice or tips for a new propliner pilot

Thanks

 

Pressurisation is paramount. And pressure RATE is most important. Most airliners of the early generation need a decent rate of no more than 1,000 ft/min, never mind what Zippy says (and there is no back up to support his theory).

1,400-1,500 ft/min is only for jets. Most propliners would cruise at 18,000-20,000 feet, jets 10K higher. Therefore they use a lower pressure differential.

[mrzippy]

Pressurisation is paramount. And pressure RATE is most important. Most airliners of the early generation need a decent rate of no more than 1,000 ft/min, never mind what Zippy says (and there is no back up to support his theory).

1,400-1,500 ft/min is only for jets. Most propliners would cruise at 18,000-20,000 feet, jets 10K higher. Therefore they use a lower pressure differential.

 

How's about if I throw in to disregard what mallcott says? Where's your proof of the pudding? I did not expunge a therory, I just told it like I flew it!

 

No wonder your posts have to go through moderation!:rolleyes:

[keefpee]

A descent rate of more than 300 fpm (or is it 800 fpm?) can cause ear problems for passengers, so the dump valves control the pressurisation rate independent of the actual aircraft rate of descent.

Keith

[mrzippy]

All interesting info, but does not help the OP who is trying to not overshoot the airport because he is not descending fast enough. I did give an explanation of starting his descent earlier than what ATC has in mind for him. That way he can descend at the recommended 700 feet/min.

 

I doubt that the JBK DC-6 has pressurization "dump valves" to worry about.

[lnuss]

A descent rate of more than 300 fpm (or is it 800 fpm?) can cause ear problems for passengers, so the dump valves control the pressurisation rate independent of the actual aircraft rate of descent.

Keith

 

Typically 500 fpm is considered the max rate that minimizes ear problems. As to pressurization controls, that control is independent of the descent rate only up to a point, that is, the point at which the aircraft's maximum pressure differential between inside and outside is exceeded. And those differentials tended to be less on piston aircraft than on jets, so the max allowable (for passengers) rate of descent will vary to some degree, depending on the specific aircraft, though I expect mallcott has the right ballpark for real life, even if it may be conservative at times.

 

For the sim, the Zipper's suggestion can work just fine, and the OP can refine things as he gets more experience and does more research.

[Cas141]

Thank you all for your inputs and assistance. I have followed them with interest. As to the FSX ATC,

I'm not so sure that it will allow me to choose a slow descent rate. Ordinarily, I do not begin the descent until told to do so. Were I to begin earlier(without being instructed), I suspect that ATC would instruct me to return to my instructed altitude..?

Let me quickly explain how I fly the jetliners. I take off and under ATC instruction, fly to cruise altitude.

Rather than fly in real time(say to USA),I take a shortcut. I go to World-MAP and then move the airplane icon to near where descent will be instructed, then I return to the flight, go to ATC and ask to resume flight plan to destination. Soon the descent instructions begin, and normally all goes well.

I will try to adapt this procedure to see if I can do this OK whilst accommodating a slow propliner descent, but I have some misgivings whether that will work.

We'll see😀

[mrzippy]

If you ever look at your ATC menu when flying, the bottom 2 lines are request altitude change either higher or lower, then if selected, how many thousands of feet change. When you request a change, ATC will normally grant the change and remember it. That will be your new altitude from then on.

[mallcott]

Thank you all for your inputs and assistance. I have followed them with interest. As to the FSX ATC,

I'm not so sure that it will allow me to choose a slow descent rate. Ordinarily, I do not begin the descent until told to do so. Were I to begin earlier(without being instructed), I suspect that ATC would instruct me to return to my instructed altitude..?

Let me quickly explain how I fly the jetliners. I take off and under ATC instruction, fly to cruise altitude.

Rather than fly in real time(say to USA),I take a shortcut. I go to World-MAP and then move the airplane icon to near where descent will be instructed, then I return to the flight, go to ATC and ask to resume flight plan to destination. Soon the descent instructions begin, and normally all goes well.

I will try to adapt this procedure to see if I can do this OK whilst accommodating a slow propliner descent, but I have some misgivings whether that will work.

We'll see������

 

Total control over ALL propliners in my library.

How do you NOT control descent..?

[toucanair1]

I don't normally post here,even though I've have been a member here for years. I did see your post come up on the flightsim.com front page news feed however and couldn't resist.

 

I used to be a Turbo-prop captain IRL and up until recently, pre Covid, flew Airbus for the airlines.

 

What kind of propliners are you talking about? pressurised (ATR Beech King Air, 1900) or unpressurised Twin-Otter, DC-3 type.

 

IF, you're talking about Pressurised types, then a lot of the posts above are incorrect and may be giving you a bum steer in the wrong direction.

 

as they say - "there's more than one way to skin a cat"

 

there are quite a few formulae and rules of thumb for getting you from the flight levels to the runway in a pressurised prop driven aircraft.

 

to work out out descent rate here's an easy on you can use:

 

Divide your Ground Speed (GS) in HALF and ADD a Zero to give you an approximate descent rate in Feet Per Minute (FPM) e.g 140KTS/2 = 70 add a zero = 700FPM and so on and so on. That will give you pretty much a 3 degree profile from top of descent all the way down the ILS which funnily enough is a 3 degree Slope!

 

Having said that, most pressurised prop companies use what is called a "Three Times Profile (3x) to work out top of descent (TOD) from cruising level.

 

3 x your height in feet eg. 24000' or FL240 to Runway Elevation (AGL) let's say airport is 1000' feet above sea level so it will be 24 -1 = 23 x 3 = 69 therefore you should expect to start your descent

69 nm in total track miles from your destination, also depending on the size of the aircraft usually to allow an extra 5 miles (69+5+74 nm) to decelerate to get your gear and flap out before you hit the top of the ILS or whatever approach you're doing.

 

Keep calculating that every mile of so and it's a good rule of thumb to see if you're high or low on descent profile. if your high just increase your rate of Descent as need and vice versa. most of the time were descending on or near the barbers pole at around 1500 to 1800 FPM depending on ride (gusts, turb, tailwind etc). just try and keep one eye on your pressurization gauge and try not to "catch your cabin".

 

Flight Sims Default ATC (P3D,FSX) will usually keep you above terrain when using IFR plans, it's a pretty clunky with vectors to final though. and doesn't give you very fluid and constant descents to lower altitudes so It's very stop start, but real ATC can be that way at times too, nothing a proficient aviator can't handle. if default ATC hasn't given you a descent clearance by the time you want to head on down, just ask for the lower altitude options, Say 5000' or 10,000' using (`) key to get you going.

 

if you have any more questions or need help, just PM me

 

hope this helps a little.

 

Cheers T.

[Cas141]

If you ever look at your ATC menu when flying, the bottom 2 lines are request altitude change either higher or lower, then if selected, how many thousands of feet change. When you request a change, ATC will normally grant the change and remember it. That will be your new altitude from then on.

 

Thank you zippy. Yes, when I tried a flight I realised that that was what I could do.And so I did.

I requested a reduced altitude, it was granted , and so I thought, cracked it.������

However, Sod's law. After an ATC instruction, the screen I had left on ATC was not one where I could choose to ask for an altitude change! All I had the choice of was to ask for a change in destination, or a change in something else (can't recall) or cancel IFR.

So I decided to ignore the ATC when they kept telling me to climb to 15000( I was descending at 700ft/min) until I got a heading instruction.I obeyed that and continued, hoping I would get the change of altitude options up.

That didn't happen, so I continued my descent!.(with incessant climb to 15000! instruction!)

The good news was that near the end when I was low, I then got an instruction to descend to 1500 together with heading direction just prior to hitting the glide slope beam.

So, I made a proper glideslope landing.

It seemed throughout the major part of the descent that I couldn't do anything to get back to the ATC texts giving me options to increase or reduce altitude.

Is there something I could have done?

Cheers

Edited June 11, 2020 by Cas141

[mrzippy]

Once ATC has ordered you to start your descent, then you will no longer have the options to ask for a decrease or increase of altitude. Your request must be made before ATC has a chance to tell you.

 

While flying jets, I ask for descent at 150 miles from destination, props at about 120 miles out.

Edited June 11, 2020 by mrzippy

[Cas141]

Total control over ALL propliners in my library.

How do you NOT control descent..?

 

Re your first sentence - " congratulations!"

 

Re the second. I thought it seemed apparent that I was referring to controlling the descent in accordance with ATC instruction AND the correct rate of descending a propliner

That difficulty I was finding was the whole point of the post. Perhaps you speed read and didn't grasp that.

Anyway, my reply to Zippy should explain it.

Perhaps you could tell me if

a) you use default ATC,

B) and if you do, exactly how do you not have the problem I am having.?.

[johnhinson]

Microsoft's ATC is not very user-friendly with descent rates and approach instructions. It calculates a point where you would start a descent at its fixed descent rate (around 700 fpm, I think) as if the airport is at sea level. This gives you plenty of time to descend at a slow rate to a high altitude airport but not to a more typical one.

 

As has been said, you can request a lower altitude before you get your landing instructions but after that you are stuck with the instructions given.

 

My solution to this problem is to take the nags away and do what I want to do! A simple edit in Editvoicepack of three files will take the nags away. Just change:

• Expedite your turn to . . .
  
• Expedite your climb to . . .
  
• Expedite your descent to . . .
  

... to a very short silent file and you will get one initial instruction and nothing more. You can then climb, descend and route yourself by your chosen approach or departure in peace.

 

In my little "virtual" world I fly nothing but pre-1970s airliners, from small piston-engined DC-3s through to hefty turbo-prop Bristoi Britannias and I really couldn't fly them any other way. I think the only thing that would fly would be the computer itself . . . through the window!

 

It is true that many piston-engined airliners climbed and descended at a sedate rate. I think it was more of a power thing than ear-concern. Turbo-props of the 1960s climbed better but some had to descend slowly owing to their weight and streamline effect to maintain speed control.

 

John

[Cas141]

Thank you very much gentlemen. This is enlightening stuff. It seems to boil down, to deciding the point of start of descent as Toucanair describes, and then, for me, tom ignore the altitude requirements of ATC until just before Glideslope.

I had wondered if there was a way to "shut up" the ATC from nagging me, and Johnhinson statement re Editvoicepack is a revalation. To the point that I don't have a clue what it is , wherebto find it or how to use it😀

I'd like to try it out. Where can I find out how to do that?

Is it an edit for all the planes' ATC, or is it done on an individual plane basis.( I'd like to keep the ATC as is for my jets)

once again, thanks to all for taking the time to help me- clearly you have spent some time on your not very short posts. It is appreciated.

.

[il88pp]

First, ATC is there to help you. Not the other way around.

They keep you safe from mid air collisions. They warn you if you deviate from the plan without telling them first, in case you are deviating or descending accidentally.

They want to know where you are going, to keep other planes safe as well.

But they don't decide what you do. The pilot always has the final decision. You tell them your plan, they help you follow it. If you want to descend early, ask fo clearance, wait to get clearance, and descend.

 

 

Second, plan your approach.

Descending to get down on time depends not only on descent rate, but also on airspeed.

Lets say you are at 21.000 ft.

You get a call to descend when 60Nm out from destination.

If you want to descend at 700ft per minute,

it will take you 21.000/700= 30 minutes to descend to ground level.

That would mean you have to fly the remaining 60Nm in 30 minutes.

And 60Nm in 30 minutes means flying 120 NM/hour. (= 120 kt)

 

same descent, but now at 1000 ft per minute would mean

21.000/1000=21 minutes.

60Nm in 21 minutes

Means your speed has to be just under 180 Nm/hour (=180 kt.)

(almost 3) x21 minutes = one hour

and

(almost 3) x 60 Nm= almost 180 Nm

So 180 Nm in one hour, (=180kt)

 

My point is, to get down in the 60 Nm, if you want to use a low verical speed, use a low horizontal speed as well.

[Cas141]

I've looked at Editvoicepack website and not sure I'll use it. (Do you have to be online to use it?)

I'm not the most tech savvy 😀. I'll see if turning down the voice sounds satisfies my wants.

Ill88p- Thanks for that. I am aware of why ATC is there😀. It's just that FSX ATC is somewhat dictatorial at times. As I explained, I found that I was descending to satisfy requirements that you explain, but I had not been able to ask for permission to descend , I couldn't get back to ATC to ask for permission, and I was getting incessant demands to climb back to 15000.

So, let's say I am at 21000 ft and I decide to descend at the rate you say. I ask ATC before permision to descend, and that can be at a max of 10000 , yes?.

If granted, then are you saying that FSX ATC will accommodate that descent rate , and will not give me conflicting instructions? That when I get to 11000 ft the ATC will fall in with what I'm doing (to get me to just prior to glideslope heading instruction ) at MY rate of descent of 700ft, ?

(Note- Zippy above says that I may not be able to ask again for a altitude reduction)

I'm thankful for your calculation examples and I will look forward to using them in my next few flights.

where I will await with interest what default ATC does😉

 

 

BTW, anyone. Is there a way, within FSX , where I can edit the default ATC, using a config or something.

Like, eliminating certain instructions.

[mrzippy]

Default ATC is a little funky sometimes. (known by most who use FSX!) That being said, ATC does not care how fast you descend to a requested altitude but will nag you if you are too slow to do so. They will also nag you to death about being 300 feet to high or 400 feet too low of the assigned altitude. One other little niggle is that at certain airports, Palm Springs, Calif. for example, They tend to bring you in over the mountains before turning on to final approach. You are at 8,000 and three miles from touchdown!! I call it "diving for the runway" !

 

There are alternate addon programs to replace default ATC and also VATSIM, where you actually talk to a member who is acting as ATC.